If you're looking to use a Linux board for web stuff in the Arduino ecosystem, there's the Rascal (disclosure: which I built): http://rascalmicro.com . If you expect to be compiling your own kernel and that sort of thing, the Beagleboard is slightly cheaper, as noted in another comment.

I'd go with a $149 BeagleBoard-XM if you want the DVI, or an $89 beaglebone if you don't need video.

For $149 I'd rather get an i.MX53 Quick Start Board with Cortex-A8 @ 1 GHz / 1GB DDR3 RAM / SATA(!) / 1080p video decoder / VGA / Ethernet / USB.

I agree about BeagleBone, it's a great choice if you don't need video or too much RAM, and it includes a JTAG adapter.

Just a warning: the illustration on the page shows an attached display. You don't get the LCD & touchscreen in the $149 price. That's another $199 for the 4.3" resistive, and $499 for the 10.1" procap. OUCH.